1. Field
This invention relates generally to fast wake-up and link acquisition, and more particularly to fast wake-up and link acquisition in reduced-twisted pair gigabit Ethernet applications.
2. Related Art
Automotive Area Networks (AANs) allow interconnection of multiple devices via a network implemented in an automobile. AANs are similar to more traditional local area networks (LANs), but often have more stringent startup time requirements for networked devices. Many AANs are currently implemented using controller area network (CAN) buses, which are considerably slower than LANs implementing any of the various forms of Ethernet, especially LANs implementing Gigabit Ethernet. Gigabit Ethernet traditionally requires four twisted wire pairs (“twisted pairs”), which would make automotive wiring harnesses prohibitively heavy. Thus, the IEEE has established the 802.3 Reduced Twisted Pair Gigabit Ethernet PHY study group to study using fewer than four twisted pairs to implement Gigabit Ethernet in AANs.
Gigabit Ethernet applications require the use of auto-negotiation between PHY devices to establish communication between two devices. During the auto-negotiation process the devices attempting to communicate with each other via the AAN will each send each other information about their capabilities so that a proper communication mode can be established. During the auto-negotiation process, the PHY of one device is selected as the master, and the PHY of the other device is selected as the slave.
After exiting auto-negotiation, the PHY enters a training mode. Training begins with the SLAVE silent and the MASTER at a reduced transmit power until it receives a response from the slave. PHY training is coordinated by exchanges of information using 2-level pulse amplitude modulation (PAM) signaling in “Info fields,” which are used to convey state transitions, transmit power settings, transition synchronization information, receiver status, such as signal to noise ratio (SNR), and to exchange precoder coefficients. Additionally, the link integrity can be tested at the PHY level.
Because of the relatively large amount of information that must be passed back and forth as part of the link acquisition process, current technology can require a link acquisition time that is prohibitively long in the context of AANs.